Gene expression changes in maternal, fetal, and neonatal tissues from exposure to hexafluoropropylene oxide-dimer acid (HFPO-DA, GenX)

The specific mechanisms by which per- and polyfluorinated alkyl substances (PFAS) exert developmental toxicity in laboratory animals are not well described. Existing literature has focused on activation of peroxisome proliferator-activated receptor alpha (PPARα) and perturbation of the developing fetal tissues. Here, we utilized reverse transcriptase quantitative PCR (RT-qPCR) gene expression profiling arrays covering multiple signaling pathways to identify key genes and target tissues impacted by PFAS exposure in pregnant Sprague-Dawley rats and offspring. Dams were dosed with hexafluoropropylene oxide-dimer acid (HFPO-DA; i.e., GenX) via oral gavage from gestation days (GD) 14-18 (1-500 mg/kg/d) or GD 8 – postnatal day (PND) 2 (10-250 mg/kg/d) with maternal liver and fetal tissues (liver, heart, lung, kidney, thymus) collected on GD 18 and neonatal livers collected on PND 0. Maternal, fetal, and neonatal livers all displayed significantly altered expression of genes in the PPAR signaling pathway associated with all three PPAR isoforms – α, β/δ, γ. Each tissue type had distinct expression profiles; however, 7 genes (Acadm, Acox1, Cpt1b, Ech1, Ehhadh, Fabp1, and Rxrg) were significantly upregulated in maternal, fetal, and neonatal livers. Only neonatal livers displayed genes that were significantly downregulated (Fabp2 and Slc27a5). Neonatal livers were also assessed using a glucose metabolism pathway with 17 genes significantly downregulated including Ugp2, Aldob, and Agl. Preliminary data on PPAR pathway gene expression in additional fetal tissues indicated that the overall rank order of tissues based on number of highly affected genes was: liver>thymus>heart>lung>kidney. Ongoing research is investigating the maternal, fetal and neonatal liver expression of PPAR and glucose metabolism pathway genes from gestational exposure to a second understudied PFAS, Nafion byproduct 2 (NBP2), and a mixture of three PFAS (GenX, NBP2, and perfluorooctane sulfonate (PFOS)). Abstract does not necessarily reflect US EPA policy.

Impact/Purpose

Per- and poly-fluoroalkyl substance (PFAS) research is an area of critical need due to the extreme environmental persistence, widespread occurrence, long biological half-lives, and nearly ubiquitous human and environmental exposure to this chemical class. Perfluoroalkyl ether acids (PFEAs) are a sub-class of PFAS and include the compounds hexafluoropropylene oxide dimer acid (GenX) and Nafion byproduct 2 (NBP2). PFEAs are currently used in the production of fluoropolymers following the phase-out of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), presumably due to more favorable fate and toxicity profiles. However, monitoring studies have detected GenX, NBP2, PFMOAA, and others in a wide range of matrices including surface water, drinking water, and/or human serum. Little to no published research is available regarding the potential toxicity of these compounds compared to the legacy PFAS. The data reported here indicate that additional signaling pathways, besides PPAR signaling, are highly involved in the adverse developmental effects of in utero PFAS exposure. Further, it also appears that the liver is the most responsive organ in the fetus (in terms of gene expression changes), but multiple other organs are involved, as well. Finally, this data will be highly informative for investigating and informing the development of AOPs that are relevant to the developmental toxicity of PFAS. The data from this project will be useful to state, federal, and other regulatory agencies in the interpretation of toxicity data and the development of hazard/risk assessments for GenX and other PFAS.

Citation

Lambright, C., N. Evans, M. Cardon, E. Medlock Kakaley, V. Wilson, J. Conley, AND L. Gray. Gene expression changes in maternal, fetal, and neonatal tissues from exposure to hexafluoropropylene oxide-dimer acid (HFPO-DA, GenX). Society of Toxicology Annual Meeting-Virtual -Webinar, Anaheim, CA, April 30, 2020.